Non ablative, state changeable, optical data storage systems record information in a state changeable material that is switchable between at least two detectable states by the application of energy thereto, for example, the application of projected beam energy such as optical energy, particle beam energy or the like.
The state changeable optical data storage material is present in an optical data storage device having a structure such that the optical data storage material is supported by a substrate and encapsulated in encapsulants. The encapsulants may include anti-ablation materials and layers, thermal insulating materials and layers, anti-reflection layers between the projected beam source and the data storage medium, reflective layers between the optical data storage medium and the substrate, and the like. Various layers may perform more than one of these functions. For example, the anti-reflection layers may also be thermal insulating layers. The thicknesses of the layers, including the layer of state changeable data storage material, are optimized whereby to minimize the energy necessary for state change while retaining the high contrast ratio, high signal to noise ratio, and high stability of the state changeable data storage material.
The state changeable material is a material capable of being switched from one detectable state to another detectable state by the application of projected beam energy thereto. State changeable materials are such that the detectable states may differ in their morphology, surface topography, relative degree of order, relative degree of disorder, electrical properties, and/or optical properties, and that they be detectable therebetween by the electrical conductivity, electrical resistivity, optical transmissivity, optical absorbsion, optical reflectivity and any combination thereof.
The optical data storage material is typically deposited as a disordered material and formed or initialized to a system having relatively reproducable erased or "0" crystalline properties and relatively reproducable written, binary "1" amorphous detectable properties with a relatively high degree of history invariant discrimination therebetween for a high number of write-erase cycles, i.e. for a relatively high number of vitrify-crystallize cycles.
Deposition may be by evaporative deposition, chemical vapor deposition, or plasma deposition. As used herein plasma deposition includes sputtering, glow discharge, and plasma assisted chemical vapor deposition. The resulting as deposited disordered material must be initialized as described for example in the commonly assigned copending application Ser. No. 667,294 of Rosa Young and Napoleon Formigoni, filed Nov. 1, 1984, for Method Of Forming An Optical Data Storage Device. That is, the memory must be conditioned, formed, initialized, or otherwise prepared to receive data if the data is going to be recorded in a disordered ("binary") state. Initialization, i.e. formation, requires the conversion of the phase changeable data storage material from the as deposited disordered state to a stable system switchable between a vitrified, disordered, written state corresponding to binary 1 and an ordered "erased", crystallized state corresponding to binary "0" with history invariant cycling properties.
Present systems are multiphase systems where the ordering phenomena includes a plurality of solid state reactions to convert a system of disordered materials to a system of ordered and disordered materials, and where the vitrification phenomena includes solid-solid, solid-liquid, and liquid-liquid reactions, including reactions at phase interfaces, whereby to convert a system of disordered and ordered components to a system of disordered components. The above phase separations occur over relatively small distances with intimate interlocking of the phases and gross structural discrimination.
Exemplary of this reacting system is the reaction of the prior art disordered germanium-tellurium-oxygen systems under "crystallizing" conditions to form germanium oxide, germanium dioxide, tellurium, and different germanium-tellurium compounds where the tellurium is crystalline. The reactions are characterized by the buildup of stable germanium oxides which do not consistently react with the germanium-tellurium components on vitrification. The buildup of germanium oxides, within the memory material is, for the energies of interest, relatively irreversible. This is because of the high melting temperatures and stability of the oxides. This ultimately leads to a cycle history dependancy as oxide builds up and "erase-write" discrimination changes over the number of cycles.